1. Field of the Invention
The present invention relates to a secondary battery such as a lithium secondary battery and a fabrication method through which the secondary battery is manufactured.
2. Description of Related Art
Among lithium secondary batteries with large capacities (Wh) developed in recent years as motive power sources in hybrid vehicles, electric vehicles and the like, particularly intense interest is focused on prismatic lithium secondary batteries assuring high energy density (Wh/kg).
A prismatic lithium secondary battery includes a flat jelly roll constituted with a winding assembly of a positive electrode formed by coating a positive foil with a positive active material, a negative electrode formed by coating a negative foil with a negative active material and a separator that prevents contact between the positive electrode and the negative electrode. The jelly roll, which is housed in a case, and a positive electrode connector terminal and a negative electrode connector terminal disposed at a lid so as to be exposed to the outside are electrically connected with the jelly roll via current collector plates. The case and the lid are welded together and thus sealed and after an electrolyte is injected through an injection opening located at the lid, the injection opening is sealed through welding.
Japanese Laid Open Patent Publication No. 2009-259524 discloses a battery manufactured by inserting a cylindrical connector terminal via through holes formed at an external terminal, an insulating member, a lid and a gasket respectively, locking the individual members through swaging onto the connector terminal which is widened toward the outer circumferential side from its central axis and fusing the outer circumferential edge of the swaged portion of the connector terminal with the external terminal through spot laser welding.
Japanese Laid Open Patent Publication No. S 62-254992 discloses an aluminum laser welding method implemented in an oxygen-containing atmosphere, which assures a greater penetration depth of weld achieved by lowering the reflection rate with which the laser beam is reflected, via an oxide layer.